Georges Cuvier (1769-1832) was a French naturalist who did not support the theory of evolution describing the gradual changes of the species. As a result, he argued for the constancy of the species. Cuvier used comparative anatomy to classify multiple extinct species. As a result, the principles of his work form the basis of the comparative anatomy and paleontology. Cuvier carried research on fossil animals (i.e., mastodons and mammoth) of the Parisian basin. This work led him to the theory of catastrophes, according to which each geological period had specific animal and plant species. Each period ended with a significant species catastrophe when most of the species died, and new species emerged replacing the old ones.